1. Field of the Invention
The present invention relates to the field of digital systems. More specifically, the present invention relates to hubs of peripheral buses.
2. Background Information
With the advances in microprocessor technology, today""s personal computers possess computing power that rivals the capabilities of mainframe computers of past years. The advances had also led to increasing number of electronic appliances, such as set-top box, and other entertainment systems. Increasingly, these computers and electronic appliances are used for multi-media applications, involving isochronous data, such as audio and video. Together, these isochronous data impose a large aggregate bandwidth requirement on the peripheral bus, to which the isochronous peripheral devices are attached. Examples of isochronous devices include cameras, speakers, microphones, scanners, and so forth.
A number of peripheral bus technologies are known in the art. Universal Serial Bus (USB) is an hierarchical serial bus technology developed in recent years to provide a low cost and easy-to-use solution to meet multi-media application bandwidth requirement. To achieve the low cost and easy-to-use objectives, USB supports only a xe2x80x9cfull speedxe2x80x9d signaling rate of 12 Mb/s and a xe2x80x9clow speedxe2x80x9d signaling rate of 1.5 Mb/s. To accommodate the xe2x80x9clow speedxe2x80x9d devices on the peripheral bus, speed shifting is performed on a packet boundary basis when alternating between the xe2x80x9cfull speedxe2x80x9d and the xe2x80x9clow speedxe2x80x9d devices. Experience has shown that this is a significant performance burden to the xe2x80x9cfull speedxe2x80x9d devices, and a waste of bandwidth. Moreover, recent experience has further shown that even greater bandwidth is required to support the ever increasing number and varieties of isochronous peripheral devices users are interested in.
Another popular peripheral bus technology is the Firewire or IEEE 1394 serial bus technology (IEEE 1394, High Performance Serial Bus, 1995). 1394 supports multiple signaling rates, up to 400 Mb/s. While the aggregate bandwidth is substantially higher than USB, 1394 is fundamentally a more costly technology. Moreover, it too employs the above mentioned wasteful speed shifting approach to accommodate the slower speed devices.
Thus, an improved approach to provide the desired increase in bandwidth, yet backward compatible to some of the lower cost solutions, such as USB, and unencumbered by the disadvantages of the prior art, is desired.
A novel I/O peripheral device is disclosed. The I/O peripheral device includes buffering circuitry to buffer request packets destined for a bus agent, received from a bus controller in an integrated multi-packet form, in bulk, and at a first communication speed. Furthermore, the I/O peripheral device includes control circuitry to forward the request packets separately, in a packet-by-packet basis, to the first bus agent, in a second communication speed.